MuJoCo

Simulusion includes convenience factories for Gymnasium MuJoCo environments, currently focused on configurable Humanoid and HalfCheetah creation. These factories return standard Gymnasium environments; wrap them with GymImageEnv if a Simulusion model needs image observations.

Install: pip install "gymnasium[mujoco]"

Humanoid factory

from simulusion import make_mujoco_env

env = make_mujoco_env(
    "Humanoid-v4",
    forward_reward_weight=1.25,
    ctrl_cost_weight=0.1,
    contact_cost_weight=5e-7,
    healthy_reward=5.0,
    terminate_when_unhealthy=True,
    healthy_z_range=(1.0, 2.0),
)

The factory builds Humanoid-{version} and forwards common reward, reset, health, and observation-component parameters to Gymnasium.

HalfCheetah factory

from simulusion import make_mujoco_env

env = make_mujoco_env(
    "HalfCheetah-v4",
    forward_reward_weight=0.1,
    reset_noise_scale=0.1,
    exclude_current_positions_from_observation=True,
    render_mode="rgb_array",
)

The factory builds HalfCheetah-{version} and forwards the selected reward, reset, observation, and render parameters.

Using MuJoCo with Dreamer-style image observations

Because the MuJoCo factories return raw Gymnasium environments, wrap the environment with GymImageEnv or configure Dreamer through the Gym backend:

from simulusion import DreamerConfig

cfg = DreamerConfig()
cfg.env_backend = "gym"
cfg.env = "HalfCheetah-v4"
cfg.gym_render_mode = "rgb_array"

For custom factory output:

from simulusion import GymImageEnv
from simulusion import make_mujoco_env

base_env = make_mujoco_env("HalfCheetah-v4", render_mode="rgb_array")
env = GymImageEnv(base_env, seed=0, size=(64, 64))

Observation and action contract

Raw MuJoCo factories expose Gymnasium's default MuJoCo observations and continuous Box actions. GymImageEnv converts observations/renders into {"image": (3, H, W)} and keeps continuous action bounds from the base environment.

Troubleshooting

• Import or renderer errors: install gymnasium[mujoco] and validate local MuJoCo rendering.
• Missing images: pass render_mode="rgb_array" for environments that support rendering.
• Action normalization: raw factories do not normalize actions; Dreamer make_env() adds NormalizeActions only when using the configured backend path.